1. Field of the Invention
The present invention relates to an electrical shield structure between an electronic device unit such as a numerical control device and a control panel housing.
2. Description of the Related Art
An electronic device unit which controls a machine tool, such as a numerical control device, is mounted on a control panel housing or the like of the machine tool and is used in a severe factory environment in which a cutting fluid is used. Therefore, the cutting fluid may be directly or indirectly applied to the electronic device unit. Therefore, for the purpose of protecting the inside of the control panel housing from the factory environment, a structure in which a seal member such as a packing is used between the control panel housing and the electronic device unit or in a pull-in port of a cable directed to the inside of the control panel housing so as not to allow outside air or the cutting fluid to infiltrate into the control panel housing is formed.
On the other hand, the electronic device unit needs to maintain noninterference with and resistance (EMC) to electrical noise such as electromagnetic waves, radiation noise, or induction noise, and thus an electrical shield needs to be provided between the control panel housing and the electronic device unit as an EMC countermeasure. In order to allow physical sealability and an electrical shielding effect to be compatible with each other as such, a conductive packing has been hitherto used as the seal member.
FIGS. 7 and 8 are views illustrating the structures of a control panel housing and an electronic device unit of the related art.
As illustrated in FIG. 7, an electronic device unit 1 such as a display unit or an operation panel unit is used in a state of being mounted on a control panel housing 2 in a factory environment. FIG. 8 is a view illustrating the electronic device unit 1 detached from the control panel housing 2 when viewed from the rear side. The electronic device unit 1 is configured by allowing an electronic component such as a display panel or a substrate to be embedded in a metal frame 4. The metal frame 4 is provided with mounting portions 5, for example, at the four corners thereof such that the metal frame 4 can be mounted on the control panel housing 2 by the mounting portions 5. In addition, a conductive packing 10 is attached between the metal frame 4 and the control panel housing 2, and the metal frame 4 is mounted on the control panel housing 2 by allowing the mounting portions 5 to pass through holes 7 provided in the conductive packing 10 such that the gap between the metal frame 4 and the control panel housing 2 is sealed by the conductive packing and thus infiltration of a cutting fluid or the like into the control panel housing 2 is prevented. In addition, the metal frame 4 and the control panel housing 2 come into contact with each other via the conductive packing 10, and thus an electrical shield which electrically shields an electronic component from an outside factory environment is formed.
In addition, as other EMC countermeasures, as described in JP 07-326881 A, a structure in which an electrical shield is obtained by providing predetermined embossed portions (protrusions) is known.
However, the conductive packing is more expensive than a general packing, and thus there is a problem in terms of cost. In addition, an electrical shield structure described in JP 07-326881 A relates to an electrical shield structure of a component in a device. Therefore, a seal member such as a packing which is an insulating material is not disposed between components included in the electrical shield structure. Although such a configuration is simply employed by a machine tool, there is a problem in that physical sealability may not be secured.